Project Summary/Abstract The objective of this project is to develop a novel detector technology that can yield significant improvements in clinical time-of-flight positron emission tomography (TOF PET) scanners by improving the coincidence time resolution (CTR) of PET detector modules. The main benefit of improved CTR in TOF PET scanners is allowing time-of-flight information to be incorporated into the time-of-flight reconstruction, leading to a large improvement in the signal-to-noise ratio (SNR). Investigations performed over the last decade using both physical phantoms and clinical studies have shown that this improvement can be used to improve the imaging performance of PET, through a combination of improved lesion detectability, reduced scan time or injected dose, and more accurate and precise tumor uptake measurements. The clinical benefits of TOF PET have been clearly demonstrated, but the ultimate benefits of TOF PET have yet to be realized because the CTR of current commercial TOF PET scanners is still limited to about 400?500 ps fwhm. All commercial PET detector modules read out the scintillation light from only one end of the crystal (i.e., single-ended readout), which has two serious limitations when applied to practical system using long efficient crystals: 1) they do not measure depth-of-interaction (DOI) and cannot compensate for variations in annihilation and optical photon transit times; and 2) the spatial resolution is limited because they do not compensate for parallax error away from the center of the imaging field. The proposed detector technology using dual-ended readout overcomes both of these limitations by correcting for all depth-dependent effects and using a better statistical approach in estimating the arrival time. As a result, significant improvement can be achieved in the CTR and DOI resolution. The motivation for this project is based on our recent simulation studies that show that reading the scintillation light from both ends of the crystal (i.e., dual-ended readout) with high-performance silicon photomultiplier (SiPM) photodetectors will lead to detector modules with unprecedented CTR for TOF PET applications. We expect to achieve at least a factor of two improvement in the SNR, which corresponds to a factor of four improvement in the sensitivity. We will accomplish this through a combination of advanced fast scintillator materials, high-performance SiPM photodetectors, high-performance readout electronics, and an algorithm based on the inverse variance weighted average to give the best time resolution in an innovative dual-ended readout detector module. The outcome of this proposal will be high-performance TOF PET detector modules with a dramatic improvement in the time resolution, which is needed to justify the development of the next generation of clinical TOF PET scanners.